Groovy Goodness: Add Some Curry for Taste - Messages from mrhaki-优快云博客

本文介绍Groovy语言中使用curry()方法克隆闭包并固定部分参数的技术。通过实例展示了如何利用该技术简化代码，包括加法运算、列表过滤及文本查找等应用场景。

Currying is a technique to create a clone of a closure and fixing values for some of the parameters. We can fix one or more parameters, depending on the number of arguments we use for the curry() method. The parameters are bound from left to right. The good thing is we can even use other closures as parameters for the curry() method.

Let's see some curry() action in the following sample:

      00.
      // Simple sample.
     
      01.
      def addNumbers = { x, y -> x + y }
     
      02.
      def addOne = addNumbers.curry(1)
     
      03.
      assert 5 == addOne(4)
     
      04.
       
      05.
       
      06.
      // General closure to use a filter on a list.
     
      07.
      def filterList = { filter, list -> list.findAll(filter) }
     
      08.
      // Closure to find even numbers.
     
      09.
      def even = { it % 2 == 0 }
     
      10.
      // Closure to find odd numbers.  
     
      11.
      def odd = { !even(it) }  
     
      12.
      // Other closures can be curry parameters.
     
      13.
      def evenFilterList = filterList.curry(even)
     
      14.
      def oddFilterList = filterList.curry(odd)
     
      15.
      assert [0,2,4,6,8] == evenFilterList(0..8)
     
      16.
      assert [1,3,5,7] == oddFilterList(0..8)
     
      17.
       
      18.
       
      19.
      // Recipe to find text in lines.
     
      20.
      def findText = { filter, handler, text -> 
     
      21.
          text.eachLine {
     
      22.
              filter(it) ? handler(it) : null
     
      23.
          }
     
      24.
      }
     
      25.
      // Recipe for a regular expression filter.
     
      26.
      def regexFilter = { pattern, line -> line =~ pattern }
     
      27.
       
      28.
      // Create filter for searching lines with "Groovy".
     
      29.
      def groovyFilter = regexFilter.curry(/Groovy/)
     
      30.
      // Create handler to print out line.
     
      31.
      def printHandler = { println "Found in line: $it" }
     
      32.
       
      33.
      // Create specific closure as clone of processText to
     
      34.
      // search with groovyFilter and print out found lines.
     
      35.
      def findGroovy = findText.curry(groovyFilter, printHandler)
     
      36.
       
      37.
      // Invoke the closure.
     
      38.
      findGroovy('''Groovy rules!
     
      39.
      And Java?
     
      40.
      Well... Groovy needs the JVM... 
     
      41.
      ''')
     
      42.
       
      43.
      // This will output:
     
      44.
      // Found in line: Groovy rules!
     
      45.
      // Foudn in line: Well... Groovy needs the JVM...